With rapidly increasing demand for micro projectors, there are more and more manufacturers that are directing their resources and funding toward the related researches in order to establishing a leading position in this promising and profitable technology. It is noted that micro projectors can be integrated into all kinds of electronic devices, such as cellular phones and notebook computers. By a modularization design of micro projector, any cellular phone can be equipped with a projector module and thus can be used in briefing easily and conveniently that is comparatively much more capable of attracting consumer interest than those without. Most micro projectors that are currently available on the market are flat in appearance, and consequently, all the components used in micro projectors are designed solely for reducing the thickness of the micro projectors, by that not only the flat and thin micro projectors can be portable, but also can be easily integrated with other products.
One of the key issues for producing a good micro projector is to have a refection mirror that can be driven to rotate within a large angular range and at high rotation frequency. For a XGA projector displaying a resolution of 800 pixels by 600 pixels to achieve 30 frames per second, its fast axis must be capable operating at 18 kHz or higher, and the faster the better. Conventionally, there are three different methods for actuating reflection mirrors in micro projectors, which are an electromagnetic-actuated method, an electrostatic-actuated method and a piezoelectric-actuated method, and accordingly, the reflection mirror should be configured differently in corresponding to the way it is being actuated.
In U.S. Pat. No. 7,442,918, a micro-electro-mechanical system (MEMS) device is disclosed, which utilizes a MEMS process for electroplating double layer planar coils simultaneously on its mirror and out ring relating respectively to the fast scan axis and the slow scan axis so as to enable the fast and the slow scan axes to be actuated by the Lorentz force induced from the interaction between the coils and the permanent magnets disposed at two opposite sides thereof as soon as the coils are charged. Moreover, in U.S. Pat. No. 7,659,918, a single-axis scanning device is disclosed, in which a reflection mirror that is disposed in the middle of the device is actuated to pivotally oscillate or rotate by the use of a piezoelectric material, or by the vibration induced surrounding the reflection mirror. In addition, there is another single-axis scanning device disclosed in U.S. Pat. No. 7,446,919, in that there are four piezoelectric elements being used for actuating a reflection mirror to rotate as the reflection mirror is disposed in the middle of the device.